The present relates to volatile liquid storage tanks and more particularly to such tanks having apparatus for reducing vapor generation when the tank is filing from the upper or top side of the tank. These tanks could include asphalt terminals, tank trucks, above ground petroleum fuel tanks, chemical storage tanks, mobile liquid storage containers, and the like. The focus of this invention will be on filling tank trucks from asphalt terminals. The invention, however, has application with other tank types as well.
Tanks can be mounted on tanker trucks or located underground at service stations. Tanker trucks are typically filled with the fluids using pumping equipment at the loading racks of marketing terminals, and underground storage tanks are typically gravity-filled from the trucks. An overfill protection device is used with each tank to disable the pumping equipment at the marketing terminals or to close a truck-mounted flow valve at the service station when the limit of the recipient tank's capacity is reached.
Detection probes are placed near sources such as gasoline or asphalt storage tanks. The probes are connected by wires to a central monitoring station which monitors the probe status. These detection probes include overfill probes.
Asphalt loading arms have a history of cold weather sticking problems. Two and three stage telescoping drop tube loading arms have been used in the past to meet this problem. Both trailers and spouts could be positioned in marketing terminals to save lane time. The telescoping drop spouts were less susceptible to cold sticking problems due to the geometry being a direct drop.
With the addition of vapor control systems and overfill protection probes, the telescoping drop loading spout configuration became more complex. The vapor control telescoping loading spouts frequently had smaller annular clearances between tubes. In colder weather, sticking problems occurred due to the smaller annular clearances. Other problems surfaced as well.